In recent years, new fine processing technologies have been developed as the integration degree of semiconductor integrated circuits (hereinafter referred to as LSIs) and the performance thereof have been becoming high. Chemical mechanical polishing (hereinafter referred to as CMP) is also one of the technologies, and is a technique used frequently in the process of producing LSIs, in particular, in the planarization of an interlayer dielectric, the formation of metal plugs, or the formation of embedded interconnections (wiring) in a multilayer interconnection forming step. This technique is disclosed in, for example, the specification of U.S. Pat. No. 4,944,836.
In order to make the performance of LSIs high, attempts of making use of copper or copper alloy as an electroconductive material which is to be a wiring material have been recently made. However, copper or copper alloy is not easily subjected to fine processing based on dry etching, which is frequently used to form conventional aluminum alloy wiring.
Thus, the so-called damascene process is mainly adopted, which is a process of depositing a copper or copper alloy thin film on an insulating film in which grooves are beforehand made, so as to embed the thin film therein, and then removing the thin film in any region other than the groove regions by CMP to form embedded wiring. This technique is disclosed in, for example, JP-A No. 2-278822.
An ordinary method of metal CMP for polishing a wiring metal, such as copper or copper alloy, is a method of: causing a polishing pad to adhere onto a circular polishing table (platen); impregnating the surface of the polishing pad with a metal polishing slurry while pushing a metal-film-formed surface of a substrate against the polishing cloth surface; and rotating the polishing table in the state that a predetermined pressure (hereinafter referred to as a polishing pressure) is applied thereto from the rear surface of the polishing pad to the metal film, thereby removing convex regions of the metal film by effect of relative mechanical friction between the polishing slurry and the convex regions of the metal film.
A metal polishing slurry used for metal CMP is generally composed of an oxidizer, abrasive grains, and water. As necessary, an oxidized metal dissolving agent, a protective film forming agent, and others are added thereto. The surface of a metal film is first oxidized with the oxidizer to form an oxidized layer, and the oxidized layer is shaven off the abrasive grains. This is considered to be a basic mechanism. The oxidized layer in concave regions of the metal film surface does not contact the polishing pad very much; thus, the shaving-off effect of the abrasive grains is not given thereto. Therefore, with the advance of CMP, the oxidized layer in convex regions of the metal film is removed so that the substrate surface is planarized. Details thereof are disclosed in Journal of Electrochemical Society, Vol. 138, No. 11 (1991), 3460-3464.
It is mentioned that an effective method for making the polishing rate of CMP high is the addition of an oxidized metal dissolving agent to a polishing slurry for metal films. This can be interpreted as follows: when grains of a metal oxide shaven off with the abrasive grains are dissolved into the polishing slurry (the dissolution will be referred to as etching hereinafter), the shaving-off effect of the abrasive grains increases. The addition of the oxidized metal dissolving agent produces an improvement in the polishing rate of CMP; however, when an oxidized layer in concave regions of a metal film surface is also etched so that the metal film surface is exposed uncovered, the metal film surface is further oxidized with the oxidizer. When this is repeated, the etching of the metal film in the concave regions advances. As a result, there is generated a phenomenon that a central region of the surface of metal wiring embedded after the polishing is gullied like a dish form (hereinafter, the phenomenon will be referred to as “dishing”). Thus, the planarizing effect is damaged.
For prevention thereof, a protective film forming agent is further added to the metal film polishing slurry. The protective film forming agent is an agent for forming a protective film on the oxide layer on the metal film surface to prevent the oxidized layer from being etched. The protective film is desirably removed easily by the abrasive grains without deterioration in CMP polishing rate.
In order to restrain the dishing or etching of a metal film to form LSI wiring high in reliability, suggested is a method using a polishing slurry for metal films, which contains an aminoacetic acid, glycine, or amidesulfuric acid as an oxidized metal dissolving agent, and benzotriazole as a protective film forming agent. This technique is described in, for example, JP-A No. 8-83780.
In the formation of a metal embedment, such as the formation of damascene wiring made of copper, copper alloy or the like, or the formation of plug wiring made of tungsten or the like, the following phenomena are generated when the polishing rate of a silicon dioxide film, which is an interlayer dielectric formed in regions other than the embedded regions, is also large: a phenomenon that the wiring together with the interlayer dielectric becomes thin (hereinafter referred to as erosion), and a phenomenon that the interlayer dielectric near the wiring metal regions is locally eroded out (hereinafter referred to as seams). Thus, the flatness deteriorates. As a result, an increase in the wiring resistance, and other problems are caused. It is therefore required to make the erosion and seams as small as possible.
In the meantime, below the wiring metal such as copper or copper alloy, a layer made of an electric conductor, such as tantalum, tantalum alloy or tantalum nitride, is formed as a barrier conductor layer (hereinafter referred to as a barrier layer) for preventing the diffusion of the metal into the interlayer dielectric and improving the adhesiveness. Accordingly, it is necessary to remove the exposed barrier layer by CMP in regions other than the wiring regions where the wiring metal such as copper or copper alloy is embedded. However, the conductors of the barrier layers are higher in hardness than copper or copper alloy; therefore, a sufficient polishing rate of the conductor is not obtained even with a combination of two or more out of polishing materials for copper or copper alloy, and the flatness of the polished surface becomes poor in many cases. Thus, a two-step polishing method has been investigated, which is composed of a first polishing step of polishing a wiring metal, and a second polishing step of polishing a barrier layer.
FIG. 1 illustrate schematic sectional views illustrating the formation of wiring through an ordinary damascene process. FIG. 1(a) illustrates a state before polishing, and the whole illustrated therein has an interlayer dielectric 1 having a surface in which grooves are made, a barrier layer 2 formed to follow surface concaves and convexes of the interlayer dielectric 1, and a wiring metal 3 made of copper or copper alloy and deposited to be embedded into the concaves and convexes.
As illustrated in FIG. 1(b), the wiring metal 3 is first polished with a polishing liquid for wiring-metal-polishing until the barrier layer 2 becomes exposed. Next, as illustrated in FIG. 1(c), the resultant is polished with a polishing liquid for barrier-layer-polishing until the convex regions of the interlayer dielectric 1 become exposed.
As such a polishing liquid for barrier-layer-polishing, suggested is a polishing liquid for chemical mechanical polishing which contains an oxidizer, an agent for forming a protective film on a metal surface, an acid and water, and has a pH of 3 or less wherein the concentration of the oxidizer is from 0.01 to 3% by weight (see, for example, the pamphlet of Re-Published Patent WO 01/13417).
About the two-step polishing method, the second polishing step of polishing a barrier layer may be required to have an over-polishing step of polishing the interlayer dielectric excessively in order to make the polished surface flat. An example of the interlayer dielectric is a silicon dioxide film, an organosilicate glass film which is low-k (low dielectric constant) film, or a fully-aromatic ring type low-k film. When this interlayer dielectric is over-polished, there is caused erosion, which is a phenomenon that regions where wiring metal pieces are densely arranged are excessively polished as compared with regions other than the excessively-polished regions, so that the thickness of the interlayer dielectric near the wiring metal becomes thin, or seams, wherein the interlayer dielectric near the wiring metal is locally eroded out, in accordance with the composition of the CMP polishing slurry. Thus, the flatness of the polished surface may have deteriorated to cause an increase in the wiring resistance, and other problems.
The inventors have investigated, as a method for decreasing the generation of the erosion or seams, a method using a polishing liquid containing a water-soluble polymer for protecting the surface of a wiring metal, for example, copper, and then found out that this method makes it possible to decrease the generation of the erosion or seams. However, on the other hand, the water-soluble polymer is combined with copper, which is a wiring metal, to form a copper complex on the substrate after the second polishing step, and this copper complex is adsorbed on the substrate so as to be turned to an organic residue so that the substrate is contaminated therewith. Moreover, by effect of the water-soluble polymer, the abrasive grains may be aggregated so that scratches may be generated in the polished surface of the substrate to deteriorate the flatness. When these defects are generated, inconveniences such as a short circuit, a disconnection, a fall in the yield and a fall in the reliability, are generated in the production of a high-performance semiconductor device, wherein the formation of fine wiring is necessary and indispensable.
An object of the invention is to provide a polishing slurry for metal films and a polishing method which restrain erosion and seams from being generated while a good rate of polishing an interlayer dielectric is maintained, thereby making the flatness of a surface polished therewith or thereby high. Another object of the invention is to provide a polishing slurry for metal films and a polishing method which can restrain the generation of a scratch or the generation of an organic residue on a substrate polished therewith or thereby.